The typical configuration of a four-stroke internal combustion engine comprises two or more cylinders, each comprising a piston, wherein each piston is attached to a single crankshaft. The four “strokes” consist of an intake stroke, a compression stroke, a power stroke and an exhaust stroke. During the intake stroke of a four-cycle engine the piston moves from the top of the cylinder to the bottom of the cylinder while one or more of the cylinder's intake valves are open. Fuel can be injected directly into the cylinder or can be injected over the open intake valves. This action draws the intake air mixture into the cylinder. The valves are then closed during the compression stroke which reverses the direction of the piston so that it moves from the bottom of the cylinder to the top of the cylinder, causing the air and fuel mixture to be pressurized. When the piston reaches its highest point in the cylinder, referred to as “top dead center” (TDC) and the pressure of the air-fuel mixture is maximized, a spark plug or other ignition source can then be used to ignite the fuel/air mixture, which forces the piston back down to the bottom of the cylinder. This downward movement of the piston is referred to as the “power stroke,” which causes the crankshaft to rotate and produce power which is measured in horsepower and torque. The piston's direction of motion is then reversed again, moving back towards the top of the cylinder to push the exhaust gases out of the cylinder in the exhaust stroke through one or more of the open exhaust valves. This four-stroke cycle is repeated to produce the power necessary to operate most vehicles now commercially available throughout the world.
Due to demands from the public to lower fuel consumption, as well as increased regulations from the government, car manufacturers are constantly striving for designs that improve the efficiency of its vehicles, and particularly of its vehicle's engines. Increases in fuel efficiency could easily be met by reducing engine size or power output, which in turn would decrease the amount of fuel that is needed to produce vehicle movement. However, it is generally accepted that many consumers are not willing to sacrifice performance and power for fuel efficiency. Therefore, the focus of car manufacturers has been on designing new engine configurations that provide similar or improved power output, when compared to existing engines, while at the same time improving or maintaining fuel efficiency. One design element that has been employed to achieve this purpose is the addition of a turbocharger or supercharger.
The addition of a supercharger or turbocharger provides an increase in the amount of power produced in a cylinder of a given size during the engine's power stroke. Specifically, a supercharger or turbocharger increases the amount of air (and air pressure) in the cylinder, which increases the amount of air/fuel mixture present in the cylinder when the sparkplug, or other ignition source ignites the fuel and air mixture. This increase in the amount of air present insures more complete combustion increasing the amount of power produced with each power stroke without requiring additional fuel. In this manner the engine is said to run “lean” wherein slightly more air is present than is required for complete stoichometric combustion of the fuel.
One method of increasing the air pressure within the combustion cylinder during the compression stroke involves providing air that is at a pressure higher than atmospheric pressure during the intake stroke. In normal operation, when the piston is located at bottom dead center (BDC), the air pressure within the cylinder would be close to atmospheric pressure after completion of the intake stroke. Both superchargers and turbochargers provide air that is at a higher pressure, typically six (6) to eight (8) pounds per square inch (p.s.i.) higher than atmospheric pressure. This is due to the fact that air is being pushed into the cylinder and not merely drawn into it by the vacuum created by the downward moving piston. After the intake valves are closed, the air pressure in the cylinder is already at a pressure higher than atmospheric pressure even before the piston has begun its compression stroke. As discussed above, more highly pressurized air results in a greater amount of fuel/air mixture present when ignition occurs, which results in increased power per cubic inch of engine displacement produced by each power stroke.
Although many supercharging and turbocharging systems have been utilized and designed, these presently available systems have drawbacks. For example, turbochargers are known to have lag meaning pressing on the accelerator does not immediately cause a turbocharger to work effectively and the response in increased acceleration is delayed. This is due to the fact that turbochargers depend upon exhaust gases to drive the impellers which force intake air into the engine. Superchargers do not rely on exhaust gases to drive them, meaning that many of the problems associated with turbochargers do not apply to superchargers, however, superchargers typically have their own drawbacks. For example, superchargers, sometimes referred to as “blowers,” are typically large, heavy and contain many moving parts which require more horsepower to drive the supercharger mechanism. Some of these moving parts require precision manufacturing, which can be costly and susceptible to damage and wear. Additionally, many superchargers are extremely loud and require sound dampening features which only add to the supercharger's size and weight. Superchargers are typically actuated by a belt or chain which pulls power from the motor and all belts and chains are subject to wear and stretching, which can lead to inefficiency and potential failure of the supercharger.
What is needed is an engine design that allows for an increased amount of fuel/air mixture in each combustion cylinder, as compared with normally aspirated engines, but which does not comprise the drawbacks of either currently available supercharged or turbocharged engines.